369.3 🏥 內科專科考前版

369.3.1 Mechanistic Deep Dive

369.3.1.1 Anterior Horn Cell Diseases

  • ALS (sporadic + familial)
  • SMA (5q SMN1)
  • Poliomyelitis
  • PMA, PLS (motor neuron variants)
  • Post-polio syndrome
  • Kennedy disease (X-linked bulbospinal)

369.3.1.2 NMJ Disorders

  • MG (postsynaptic, AChR/MuSK Abs)
  • LEMS (presynaptic, VGCC Abs)
  • Botulism (presynaptic, toxin)
  • Congenital myasthenic syndromes
  • Organophosphate poisoning

369.3.1.3 Periodic Paralyses

  • Hypokalemic (CACNA1S, SCN4A)
  • Hyperkalemic (SCN4A)
  • Andersen-Tawil
  • Thyrotoxic PP (Asian males with hyperthyroidism)

369.3.2 Recent Trials & Updates

369.3.2.1 MG Treatment (Detailed in Ch383)

  • Efgartigimod (Vyvgart) — FcRn inhibitor, FDA 2021
  • Rozanolixizumab (Rystiggo) — FcRn, FDA 2023
  • Zilucoplan (Zilbrysq) — complement C5, FDA 2023
  • Ravulizumab (Ultomiris) — complement C5, FDA 2022 for MG
  • Eculizumab (Soliris) — complement C5

369.3.2.2 ALS Treatment (Detailed in Ch383)

  • Tofersen (Qalsody) — SOD1 antisense, FDA 2023
  • Riluzole
  • Edaravone
  • AMX0035 (withdrawn 2024)

369.3.2.3 Inclusion Body Myositis

  • Distal weakness can be present (atypical)
  • Finger flexor + quadriceps
  • Treatment-resistant

369.3.2.4 Statin-Associated Myopathy

  • Common (muscle aches, mild ↑ CK)
  • Statin-induced necrotizing autoimmune myopathy (SINAM)
  • Anti-HMG-CoA reductase antibodies
  • Requires immunosuppression

369.3.3 High-Yield Specialist Points

369.3.3.1 Approach to Pure Motor Weakness

  • UMN: stroke, MS, MND
  • LMN: motor neuropathy (multifocal motor neuropathy), motor neuron disease
  • NMJ: MG, LEMS
  • Muscle: myopathy

369.3.3.2 Pseudobulbar Affect

  • UMN bulbar
  • Pathological laughing/crying
  • ALS, stroke, MS
  • Treatment: dextromethorphan-quinidine (Nuedexta), SSRI

369.3.3.3 Acute Flaccid Paralysis (AFP) Differential

  • GBS (most common)
  • Poliomyelitis (rare)
  • Enterovirus 71, EV-D68 (acute flaccid myelitis)
  • Botulism
  • Periodic paralysis
  • Tick paralysis
  • Transverse myelitis
  • Spinal cord trauma

369.3.3.4 Acute Flaccid Myelitis (AFM)

  • Enterovirus D68, A71
  • Pediatric
  • Acute asymmetric flaccid weakness
  • Resembles polio
  • Limited treatment

369.3.3.5 Myopathies Patterns

Pattern Suggests
Proximal symmetric Polymyositis, DM, IMNM, steroid, hypothyroid
Distal IBM (some), CMT4B
Scapular winging FSHD, LGMD
Calf hypertrophy DMD, Becker, LGMD
Ocular OPMD, mitochondrial
Bulbar OPMD, mitochondrial, IBM

369.3.3.6 Drug-Induced Neuromuscular Disorders

  • Aminoglycosides: NMJ blockade
  • Magnesium: NMJ blockade
  • Cocaine: rhabdo
  • Statins: myopathy, SINAM
  • Steroids: type II atrophy
  • Colchicine: vacuolar myopathy
  • Antiretrovirals: zidovudine myopathy

369.3.4 Pearls

  • Localize before etiology
  • UMN vs LMN distinction critical
  • EMG/NCS key for localization
  • CK elevated in myopathy, rhabdo
  • GBS: ascending, areflexia, after URI/GI → IVIG/PE
  • MG: fatigable, ocular/bulbar → AChR Abs, pyridostigmine + IS
  • LEMS: proximal improves with use → VGCC Abs, often SCLC
  • ALS: combined UMN + LMN, no sensory
  • Polymyositis/DM: proximal + ↑ CK + steroids
  • AFM: pediatric enterovirus